1. Field of the Invention
The present invention relates to the field of interactive multimedia communication networks, also called Full Service Networks (FSN). More specifically, the present inventions relates to apparatus/methods for insuring full utilization of a communication channel bandwidth when sending information from a cable system's headend to a plurality of set-top terminals.
2. Description of the Related Art
An early commercial installation by the Warmer Communications Company, under the brand name QUBE, provided an interactive TV cable system.
Interactive multimedia communication networks are generally known in the patent art. U.S. Pat. No. 5,093,718 to Hoarty et al, U.S. Pat. No. 5,412,720 to Hoarty, and U.S. Pat. No. 5,361,091 to Hoarty et al, all of which are incorporated herein by reference, are examples.
While the television art was initially a one-way communication art, recent developments have moved this art into the field of interactive services and applications wherein a TV set and its accompanying apparatus, such as a set-top terminal, have become interactive devices. The user can now exercise control over what is viewed on the TV, and how the selected programs are viewed. In addition, above-mentioned, copending patent application filed concurrently herewith and entitled CABLE SYSTEM SET-TOP TERMINAL HAVING IP ROUTING CAPABILITY allows a user to connect an external device, such as a personal computer (PC), to the set-top, and then communicate with a WAN network such as the Internet, or a similar WAN data link, by way of the OSI-IP protocol that is supported by the set-top.
With the advent of such advanced interactive techniques, also called a Full Service Network (FSN), the set-tops enable a cable TV system to be used for the reception of broadcast video, on-demand video, and two-way point-to-point, or set-top to set-top, communication on the Internet, etc.
In the point-to-point environment, a connection is established to the FSN's headend that includes a data vault, or a connection is established to the Internet at the headend. This connection is dedicated to the requesting user. When multiple users simultaneously engage in point-to-point activity, the resources of the FSN must be designed to support this multiple use.
One of the most critical resources of the FSN in supporting these one-way and two-way communication sessions between a headend and a multitude of set-tops that are located at the residences of multiple users is the bandwidth of the communications channel, or groups of channels, that connect the headend to the set-tops. Bandwidth must be allocated in order to provide the best service to the greatest possible number of users. In the traditional analog TV broadcast environment, the bandwidth is divided into multiple 6 MHz channels, with each channel having its own program or application. In the digital environment, one 6 MHz channel can be sliced or divided into multiple transmission pipes, with each pipe carrying a different program or application.
There are three basic ways to deliver digital data; i.e., Continuous-Bit-Rate (CBR), Variable-Bit-Rate (VBR), and Available-Bit-Rate (ABR). CBR is relatively intolerant to variability in the delay of the output signal, since a delay usually reduces the quality of the transmission to an unacceptable level.
With CBR, the user is guaranteed a high quality of service. However, when a point in time occurs during which the bandwidth is not fully utilized, for example as a result of data compression, available bandwidth is wasted.
In VBR, the transmission rate usually varies with time. Variations of VBR are available, unconstrained and constrained. Unconstrained VBR uses a large bandwidth, an example being the transmission of MPEG-2 compress data. Unconstrained MPEG-2 transmission provides a maximum quality transmission, but-at the cost of a large bandwidth that may be difficult to implement in the FSN. Constrained VBR simply puts a cap or maximum on the allowable bit rate, the cap usually being equivalent to CBR.
ABR is a service whose bit rate varies as a function of the unused bandwidth that is available at any given instance in time. ABR cannot be used in the FSN for time-critical data, such as conditional-access (CA) messages and entitlement-management-messages (EMMs). Other data, such as the above mentioned data that is less sensitive to transmission time delay from the headend to a set-top, can however be transmitted using ABR.
Above-mentioned copending patent application entitled METHOD AND APPARATUS FOR UTILIZING THE AVAILABLE BIT RATE IN A CONSTRAINED VARIABLE BIT RATE CHANNEL provides for the transmission of high-priority video data and lower-priority application data, wherein the high-priority data is transmitted at VBR, and the low-priority data is transmitted at ABR. More specifically, a selector operates to give video data a higher transmission priority than is given application data. An encoder supplies compressed VBR video data to an encoder buffer, and an encoder transmission processor reads data from the encoder buffer. A channel-rate-control circuit monitors the state of fullness of the encoder buffer with reference to a buffer fullness threshold. When the buffer fullness is less than the threshold, the encoder transmission processor is instructed to decrease the rate at which data is read from the buffer. When the state of buffer fullness later reaches the threshold, the encoder transmission processor is instructed to increase the rate at which data is read from the buffer. If, however, the buffer remains relatively full, even after the rate of the encoder transmission processor has been increased to a predetermined maximum channel rate, then the channel rate control circuit instructs the encoder to decrease the rate at which it outputs compressed data to the buffer. In this manner, the bit rate of the encoder varies in a manner not to exceed the maximum rate of the encoder transmission processor. The structure and arrangement of this copending patent application provides that the data-rate-space that at any time exists or is available between (1) the data rate at which the encoder transmission processor is operating, and (2) the maximum channel rate or maximum rate of the encoder transmission processor, is used to send the lower priority data at an ABR, wherein the magnitude of the ABR is determined by the magnitude of this data-rate-space.
The present invention generally relates to this above described copending patent application. However, the present invention provides an apparatus/method for using the bandwidth of the FSN's out-of-band (OOB) forward-control-channel (FDC), first for the CBR delivery of high priority, and then the left-over or residual bandwidth of the FDC is used for the lower priority delivery of other FSN information at an ABR.